Prior to the slab gas laser, diffusion cooled gas discharge lasers were characterized by output power per unit length of discharge and were typically limited to a maximum output power of 100 watts. The invention of the slab gas laser meant for the first time that the output power from diffusion cooled lasers could be scaled by discharge area rather than length only and could be characterized by a new figure of merit, watts output power per unit area of discharge. CO2 slab lasers of over three kilowatts are currently available commercially.
In order to maximize discharge cooling, the planar discharge of the slab CO2 laser is only typically one to two millimeters and the discharge electrodes are used as an optical waveguide. In order to stabilize the thin gas discharge and to maximize laser output power, the slab laser is driven at high frequency, which is typically 100 MHz. With this discharge driving frequency the electrical wavelength is typically comparable to the dimensions of the laser structure. Standing waves of current and voltage occur across the discharge electrodes and the resulting discharge non-uniformity causes serious degradation of laser power unless corrective measures are taken.
A method of reducing discharge non-uniformity resulting from electrical standing waves, well known in the art, is a linear array of inductors connecting the discharge electrodes along the length of the discharge. This inductor array is placed on one or both sides of the electrode. This method is limited because it is linear and eliminates the standing wave only along the length of the electrodes. State of the art slab lasers are typically long and narrow so that this linear discharge method has been adequate. Attempts to scale slab lasers to very high power to meet the requirements of modern material processing machinery has resulted in the commercialization of slab lasers of large discharge area. Maximum output power of state of the art slab lasers is however limited by the area of discharge that is currently practicable. The length of the electrodes is limited by mechanical and thermal distortion of the waveguide to about 100 cm and the width is limited by standing wave induced discharge non-uniformity to about 20 cm.
In the art, large area annular waveguide lasers have been disclosed as an alternative to planar slab lasers. A cylindrical structure is intrinsically more mechanically stable than a planar structure and a large area of discharge may be contained in a physically smaller structure than in a slab. However the annular laser has not emerged as an alternative technology to the Slab laser because of practical difficulties. The formation of standing electrical standing wave along the length and around the circumference, the structural difficulties of driving and cooling coaxial cylindrical electrodes and the difficulties associated with obtaining a coherent laser beam from an annular waveguide has thus far prevented the practical use of annular waveguide gas lasers.
A new method of electrical excitation of a slab discharge is disclosed. A two dimensional array of inductors is used to eliminate standing wave field patterns along the length and across the width of the electrodes. This method may be used to generate uniform gas discharge intensity for electrodes of arbitrary length, width and shape. The application of this new discharge balancing technique permits larger electrode area electrodes than is possible with prior art slab lasers and hence higher power.
Therefore, according to an aspect of the invention there is disclosed a laser, comprising first and second electrodes disposed adjacent each other to form a gap between them, each of the first and second electrodes extending laterally; a laser gas disposed within the gap; means to provide electrical excitation to the first and second electrodes and generate a laser discharge within the gap; mirrors defining a resonator disposed at opposed ends of the gap; and an inductor array disposed across and along at least one of the first electrode and the second electrode to reduce lateral discharge non-uniformities. The inductor array is connected to the electrode and to a ground or reference plane.
According to further embodiments of the invention, the laser is a gas slab laser with planar and preferably parallel electrodes. The resonator is preferably an unstable resonator. The inductor array is preferably connected to an external conductor acting as the ground or reference plane. In a still further embodiment, the electrodes are cylindrical and have an annular discharge gap between them. In operation, the inductors cause a distributed parallel plate resonance between the electrodes, resulting in voltage variation across the width and length of the electrodes being less than 5%.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.